Electric pump and method for producing same

ABSTRACT

An electric pump includes a pump portion including a pump housing and a gear pump which is housed in the pump housing, the pump portion suctioning and discharging a hydraulic fluid by a rotation of the gear pump. The electric pump also includes a motor portion arranged adjacent to the pump portion in a direction along an axis of the pump portion and including a rotor which rotates synchronously with the gear pump and coaxially with the axis, the motor portion including a stator which is arranged at an outer periphery of the rotor and disposed coaxially with the axis, the stator applying a rotation drive force to the rotor. The electric pump further includes a resin portion integrally surrounding at least an outer periphery of the pump housing and an outer periphery of the stator.

TECHNICAL FIELD

The present invention pertains to an electric pump and a method forproducing the same.

BACKGROUND ART

An electric pump is used for supplying hydraulic fluid to variousmovable mechanisms of a vehicle, for example. The electric pump includesa motor portion and a pump portion. In a case where the electric pump isoperated, a rotation drive force of a rotary shaft of the motor portionis transmitted to a gear pump of the pump portion. The electric pumpsuctions and discharges the hydraulic fluid by a rotation of the gearpump.

The motor portion and the pump portion of the electric pump aregenerally separately produced and are thereafter assembled on each otherso that displacement between an axis of the motor portion and an axis ofthe pump portion is minimized, i.e., concentricity serving as a degreeof displacement between the two axes is minimized. Complete coaxialitywhere the concentricity between the two axes is zero is practically notachieved. Nevertheless, in order to efficiently rotate the gear pump(electric pump) by effectively transmitting the rotation drive force ofthe rotary shaft of the motor portion to the gear pump, theconcentricity should be reduced.

Patent document 1 discloses an electric pump including a motor portionand a pump portion. In the electric pump, the motor portion includes afitting projection portion made of resin and the pump portion includes apump housing recess portion made of metal. The electric pump in Patentdocument 1 includes a spigot structure where the fitting projectionportion of the motor portion is fitted into the housing recess portionof the pump portion. As a result, the electric pump with smallconcentricity between an axis of the motor portion and an axis of thepump portion is assembled.

Patent document 2 also discloses an electric pump including a motorportion and a pump portion. In the electric pump, the motor portionincludes an annular case portion made of resin and the pump portionincludes a boss portion made of metal. The electric pump in Patentdocument 2 includes a spigot structure where, in an opposite manner tothe electric pump in Patent document 1, the boss portion of the pumpportion is fitted into the annular case portion of the motor portion sothat the electric pump with small concentricity between an axis of themotor portion and an axis of the pump portion is assembled.

DOCUMENT OF PRIOR ART Patent Document

Patent document 1: JP2013-217223A

Patent document 2: JP2009-156081A

OVERVIEW OF INVENTION Problem to be Solved by Invention

In each of the electric pumps disclosed in Patent documents 1 and 2, theprojection or the recess portion made of resin provided at the motorportion and the recess portion or the projection mad of metal providedat the pump portion are fitted to each other to obtain the spigotstructure. The electric pump is accordingly assembled so that theconcentricity between the axes of the motor portion and the pump portionis reduced. Nevertheless, because dimensional accuracy of the projectionor the recess portion made of resin is smaller than that of the recessportion or the projection made of metal, an issue is raised thatdecrease of the concentricity between the axes of the motor portion andthe pump portion is limited in a case where the projection or the recessportion of the motor portion and the recess portion or the projection ofthe pump portion are fitted to each other.

Therefore, an electric pump with small concentricity between an axis ofa motor portion and an axis of a pump portion than a known pump isdesired.

Means for Solving Problem

One embodiment of an electric pump according to the present inventionincludes a pump portion including a pump housing and a gear pump whichis housed in the pump housing, the pump portion suctioning anddischarging a hydraulic fluid by a rotation of the gear pump, a motorportion arranged adjacent to the pump portion in a direction along anaxis of the pump portion and including a rotor which rotatessynchronously with the gear pump and coaxially with the axis, the motorportion including a stator which is arranged at an outer periphery ofthe rotor and disposed coaxially with the axis, the stator applying arotation drive force to the rotor, and a resin portion integrallysurrounding at least an outer periphery of the pump housing and an outerperiphery of the stator.

According to the electric pump including the aforementionedconstruction, the stator and the pump housing are integrally held by theresin portion. Thus, concentricity between an axis of the stator and anaxis of the pump housing before the resin portion is formed may bemaintained by the resin portion. The resin portion is formed in a statewhere the concentricity between the axis of the stator and the axis ofthe pump housing is reduced, so that the concentricity between the axisof the stator and the axis of the pump housing at the electric pumpincluding the resin portion may be greatly reduced as compared to a casewhere the electric pump is assembled by a spigot structure. In a casewhere the concentricity between axes of the motor portion and the pumpportion decreases, the concentricity between the axis of the stator andan axis of the rotor of the motor portion decreases. Thus, an air gapbetween the stator and the rotor may decrease to thereby improve drivingefficiency of the motor. That is, with the same driving efficiency, anamount of usage of a magnet employed at the motor portion may decrease.

In the one embodiment of the electric pump 1, each of the pump housingand the stator includes a circular outermost configuration as viewed inthe direction along the axis. The pump housing and the stator includesame outermost diameters as each other. At this time, the resin portiondesirably includes a constant thickness in a radial direction of theresin portion.

In a case where each of the pump housing and the stator includes thecircular outermost configuration as viewed in the direction along theaxis and the pump housing and the stator include the same outermostdiameters as each other, flow resistance when the resin fills theforming die is small to thereby increase filling ability when formingthe resin portion by insert molding, for example. In addition, athickness of the resin portion in the radial direction thereof may beeasily constant. With the constant thickness of the resin portion in theradial direction, an entire periphery of the resin portion is evenlycooled so that shrinkage of the resin portion may be unlikely to occurand displacement of the axes of the stator and the pump housing may beunlikely to occur after cooling of the resin portion.

In the one embodiment of the electric pump 1, each of the pump housingand the gear pump is made of a ferrous material.

In order to stably drive the electric pump for a long period of time,each of the pump housing and the gear pump is desirably made of theferrous material with high strength. As long as the pump housing and thegear pump are made of the same material, thermal expansion coefficientsof the pump housing and the gear pump are the same as each other. Thus,in a case where a surrounding temperature varies, a clearance betweenthe pump housing and the gear pump is restrained from changing. At thistime, the ferrous material has a problem of being corroded when used incontact with outside air for a long period of time. Nevertheless,according to the electric pump including a construction where the outerperipheral surface of the pump housing is surrounded by the resinportion, the outer peripheral surface of the pump housing is inhibitedfrom contacting air. Thus, the pump housing even made of the ferrousmaterial is inhibited from being corroded. Performance and lifetime ofthe electric pump are inhibited from decreasing, which may lead tostable performance of the electric pump for a long period of time.

In the one embodiment of the electric pump 1, the pump housing includesa recess portion at an outer surface, the recess portion into whichresin of the resin portion is fitted.

According to the electric pump including the aforementionedconstruction, the resin portion and the pump housing are firmlyintegrated with each other. The pump housing is inhibited from movingrelative to the resin portion. In addition, because of the resin fittedinto the recess portion, the hydraulic oil hardly leaks to the outsideof the electric pump by flowing through a boundary between the pumphousing and the resin portion even if the hydraulic oil leaks from thegear pump.

One embodiment of a method for producing an electric pump includes astep for placing a stator in a cylindrical form onto an outer peripheralsurface of a fixed die of a forming die in a state where an innerperipheral surface of the stator makes contact with the outer peripheralsurface of the fixed die, the forming die being configured to open andclose and including the fixed die and a movable die, a step for placinga pump housing which includes a protruding portion in a cylindrical formin a state where an outer peripheral surface of the protruding portionmakes contact with an inner peripheral surface of a dent which isprovided at an upper surface of the fixed die, the dent including acircular cross-section in a direction orthogonal to an axis of the fixeddie, and a step for forming a resin portion by flowing resin into theforming die to harden the resin after the movable die is pressed againstthe fixed die to close the forming die, the resin portion integrallysurrounding at least an outer periphery of the pump housing and an outerperiphery of the stator.

Because the fixed die used for insert molding is processed by cutting,for example, processing accuracy is extremely high. Therefore,dimensional accuracy of an outer diameter of an outer peripheral surfaceof the fixed die in a column form and an inner diameter of the dent mayincrease. In addition, the concentricity between an axis of the outerperipheral surface and an axis of the dent is greatly reduced so thatthe concentricity between the axes of the stator and the pump housing ina case where the stator and the pump housing are placed onto the fixeddie may be greatly reduced. In the aforementioned state, the resinportion is formed to thereby integrate the stator and the pump housingwhile a relative position therebetween is maintained. As a result, theelectric pump with the greatly reduced concentricity may be produced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal section view illustrating a construction of anelectric pump according to an embodiment;

FIG. 2 is a cross-sectional view taken along a line II-II in FIG. 1;

FIG. 3 is a cross-sectional view taken along a line III-III in FIG. 1;

FIG. 4 is a cross-sectional view illustrating a forming process of aresin portion;

FIG. 5 is a cross-sectional view illustrating the forming process of theresin portion;

FIG. 6 is a cross-sectional view illustrating the forming process of theresin portion;

FIG. 7 is a cross-sectional view illustrating the forming process of theresin portion;

FIG. 8 is a cross-sectional view illustrating the forming process of theresin portion; and

FIG. 9 is a cross-sectional view illustrating the forming process of theresin portion.

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is explained below with referenceto the attached drawings.

1. Construction and Operation of Electric Pump

[Entire Construction]

As illustrated in FIGS. 1 to 3, an electric pump 1 is constructed by amotor portion 30, a pump portion 10 driven by the motor portion 30, acontrol portion 50 controlling the motor portion 30, and a resin portion60 provided at outer peripheries of the motor portion 30 and the pumpportion 10 to extend from the motor portion 30 to the pump portion 10.The electric pump 1 is employed for pumping lubricant at an engine of avehicle as hydraulic oil to hydraulic equipment. Alternatively, theelectric pump 1 may be applied to a hydraulic device of other than thevehicle. In addition, instead of the hydraulic oil, a medicine or achemical substance in liquid form may be used as a pumping object, forexample. The hydraulic oil serves as an example of hydraulic fluid.

[Construction of Pump Portion]

As illustrated in FIG. 1, the pump portion 10 includes a pump housing11, an internal gear pump 21 and a pump cover 40. The internal gear pump21 serves as an example of a gear pump.

The pump housing 11 is made of ferrous metallic material. The pumphousing 11 includes a columnar outer configuration. A housing portion 14including a bottom and a circular cross-section is provided at an endsurface of the pump housing 11 facing the pump cover 40. A protrudingportion 15 in a cylindrical form is provided at an opposite end surfacefrom the housing portion 14. An oil seal 26 is inserted to be positionedat an inner side of the protruding portion 15. An inlet port 12 and anoutlet port 13 are provided at a bottom surface of the housing portion14. A bearing bore 17 is provided at a center of the pump housing 11. Asillustrated in FIG. 2, an axis of the housing portion 14 is eccentric toan axis X of the bearing bore 17. A rotary shaft 25 is inserted to bepositioned within the bearing bore 17 in a state penetrating through theoil seal 26, the bearing bore 17 and an inner rotor 22 of the internalgear pump 21. The rotary shaft 25 is rotatably supported at the bearingbore 17. An axis of the rotary shaft 25 and an axis of the inner rotor22 are both coaxial with the axis X. The rotary shaft 25 and the innerrotor 22 integrally rotate with each other. The “coaxiality” in theembodiment does not only mean that displacement of plural axes (which ishereinafter referred to as concentricity) is zero but also mean that theconcentricity is approximately zero including zero.

The internal gear pump 21 which is housed in the housing portion 14includes the inner rotor 22 and an outer rotor 23. Each of the innerrotor 22 and the outer rotor 23 is made of ferrous metallic material. Asillustrated in FIG. 2, the internal gear pump 21 is constructed so thatouter teeth provided at the inner rotor 22 and inner teeth provided atthe outer rotor 23 are meshed with one another. With the rotation of theinner rotor 22, the outer rotor 23 rotates around the inner rotor 22 byfollowing the rotation of the inner rotor 22. Plural pump chambers 24 ofwhich volumes increase and decrease depending on the rotation aredefined between a teeth portion of the inner rotor 22 and a teethportion of the outer rotor 23.

As long as the outer rotor 23 of the internal gear pump 21 and the pumphousing 11 are made of the same ferrous metallic material, thermalexpansion coefficients of the outer rotor 23 and the pump housing 11 arethe same as each other. Thus, in a case where a surrounding temperaturevaries, a clearance between an inner periphery of the housing portion 14and an outer periphery of the outer rotor 23 is restrained fromchanging.

The pump cover 40 is made of resin and is arranged adjacent to the pumphousing 11. The pump cover 40 is joined to the resin portion 60 which isexplained later by welding, for example. The pump cover 40 includes thesame outer diameter as the resin portion 60. The pump cover 40 and theresin portion 60 are joined and integrated so that the internal gearpump 21 is held within the housing portion 14. The pump cover 40includes an inlet port 42 at a side opposite to the inlet port 12relative to the housing portion 14 and an outlet port 43 at a sideopposite to the outlet port 13 relative to the housing portion 14. Aninlet passage 44 extends outward from the inlet port 42 and an outletpassage 45 extends outward from the outlet port 43.

As illustrated in FIG. 2, the inlet port 42 is a curved groove and isprovided communicating with the pump chambers 24 of the internal gearpump 21 along a range where the volumes of the pump chambers 24 of theinternal gear pump 21 increase. In the same manner, as illustrated inFIG. 2, the outlet port 43 is also a curved groove and is providedcommunicating with the pump chambers 24 of the internal gear pump 21along a range where the volumes of the pump chambers 24 of the internalgear pump 21 decrease. The inlet port 12 includes the same configurationand the same size as the inlet port 42. The outlet port 13 includes thesame configuration and the same size as the outlet port 43.

[Construction of Motor Portion]

As illustrated in FIG. 1, the motor portion 30 is arranged adjacent tothe pump portion 10 in a direction along the axis X. The motor portion30 includes a sensorless brushless DC motor 31. As illustrated in FIGS.1 and 3, the sensorless brushless DC motor 31 is constructed by a rotor36 in a cylindrical form and a stator 32 in a cylindrical form, thestator 32 being arranged at an outer periphery of the rotor 36 with asmall clearance therebetween in a radial direction. The rotor 36 and thestator 32 are both coaxial with the axis X. The stator 32 includes anoutermost diameter which is the same value as an outermost diameter ofthe pump housing 11.

The rotor 36 is obtained by a magnet 38 embedded and fixed in a rotorcore 37 including a cylindrical form, the rotor core 37 being formed bylaminated magnetic steel sheets. The rotor 36 integrally rotates withthe rotary shaft 25. The stator 32 includes a stator core 33 formed bylaminated magnetic steel sheets, a coil support frame 35 formed by aninsulator such as resin, for example, which covers teeth of the statorcore 33, and a coil 34 wound at the teeth from above the coil supportframe 35. The coil 34 constitutes a three-phase winding, each phase ofthe coil 34 being applied with a three-phase alternating current by anelectric power supply from the control portion 50 at an outside which isexplained later. The sensorless brushless DC motor 31 does not include amagnetic pole sensor such as a Hall element, for example. The sensorlessbrushless DC motor 31 detects a rotation position of the rotor 36 byutilizing an induced voltage induced to the coil 34 by the rotation ofthe rotor 36 and switches the power supply to the phases of thethree-phase winding based on magnetic position information obtained on abasis of the rotation position of the rotor 36. The teeth of the statorcore 33 magnetized by the power supply to the coil 34 and the magnet 38are repeatedly suctioned and repelled to thereby rotate the rotor 36.With the rotation of the rotor 36, the inner rotor 22 rotates via therotary shaft 25. Accordingly, the stator 32 applies a rotation driveforce to the rotor 36.

[Construction of Control Portion]

The control portion 50 is arranged adjacent to the motor portion 30 inthe direction along the axis X. As illustrated in FIG. 1, the controlportion 50 is constructed by implementation of an electric power controlelement, a capacitor, a resistor and a control component such as a motordriver for deciding timing of power control, for example, on a controlboard 52. The control board 52 is mounted and fixed to the resin portion60 which is explained later by screwing, for example. The controlportion 50 functions to generate a rotating magnetic field bysequentially supplying the electric power to the coil 34 so as tocontrol a rotating speed of the rotor 36 by controlling a rotation speedof the rotating magnetic field. The control portion 50 is covered by acover member 54 mounted to the resin portion 60 by welding, for example.

[Construction of Resin Portion]

As illustrated in FIG. 1, the resin portion 60 is provided at outerperipheral surfaces of the stator 32 of the motor portion 30 and thepump housing 11 of the pump portion 10 to extend from the stator 32 tothe pump housing 11. The resin portion 60 surrounds the outer peripheralsurface of the pump housing 11 and surrounds the stator core 33 exceptfor a part of the teeth thereof facing the rotor 36, the coil 34 and theentire coil support frame 35. A thickness of resin of the resin portion60 at a radially outer side of an outermost circumference of the stator32 and of an outermost circumference of the pump housing 11 is constant.The motor portion 30 and the pump portion 10 are integrated by the resinportion 60. The resin portion 60 is formed by insert molding at thestator 32 and the pump housing 11. In the electric pump 1, because themotor portion and the pump portion are not combined by a spigotstructure, a clearance is formed between an outer periphery of theprotruding portion 15 of the pump housing 11 and an inner periphery ofthe resin portion 60 facing the aforementioned outer periphery in theradial direction. Details of forming method of the resin portion 60 byinsert molding are explained later.

Plural groove portions 16 each of which includes an annular form areprovided at an outer surface of the pump housing 11. The resin of theresin portion 60 is fitted into the groove portions 16. Thus, the resinportion 60 and the pump housing 11 are firmly integrated with eachother. The pump housing 11 is inhibited from moving relative to theresin portion 60. In the present embodiment, the groove portions 16 areprovided at the pump hosing 11. Alternatively, instead of the grooveportions 16, knurls including shallower groove portions than the grooveportions 16, for example, may be provided. The resin of the resinportion 6 is also fitted into the groove portions of the knurls tothereby firmly fix the resin portion 60 and the pump housing 11 to eachother. Each of the groove portions 16 and the groove portions of theknurls serves as an example of a recess portion.

Because of the resin fitted into the groove portions 16, the hydraulicoil hardly leaks to the outside of the electric pump 1 by flowingthrough a boundary between the pump housing 11 and the resin portion 60even if the hydraulic oil flows from the internal gear pump 21 through aclearance between the rotary shaft 25 and the bearing 17 and leaks fromthe oil seal 26. This is because the hydraulic oil leaking from the oilseal 26 reaches the outside of the electric pump 1 via the grooveportions 16 when flowing through the boundary between the pump housing11 and the resin portion 60, a creepage distance by which the hydraulicoil reaches the outside of the electric pump 1 is elongated as comparedto a case where the groove portions 16 are not provided. As a result,without usage of a component such as an annular seal, for example, forinhibiting leakage of the hydraulic oil, the leakage of the hydraulicoil to the outside of the electric pump 1 may be effectively inhibited.The electric pump 1 may be constructed at a low cost accordingly.

[Operation of Electric Pump]

Next, an operation of the electric pump 1 is explained. The coil 34 ofthe stator 32 is applied with the three-phase alternating current by acommand from the control portion 50 to thereby rotate the rotor 36. Withthe rotation of the rotor 36, the inner rotor 22 of the internal gearpump 21 rotates via the rotary shaft 25. When the inner rotor 22rotates, the outer rotor 23 which is meshed with the inner rotor 22rotates by following the rotation of the inner rotor 22. The volumes ofthe pump chambers 24 increase within the range where the pump chambers24 are in communication with the inlet ports 42 and 12 and decreasewithin the range where the pump chambers 24 are in communication withthe outlet ports 43 and 13 based on the rotations of the inner rotor 22and the outer rotor 23. According to the aforementioned pump operationof the internal gear pump 21, the hydraulic oil which flows through theinlet passage 44 is suctioned to the pump chambers 24 from the inletport 42 by a negative pressure and is thereafter pumped out to theoutlet port 43 from the inlet port 42 by a positive pressure so as toflow through the outlet passage 45 by being discharged from the outletport 43.

2. Assembly Method of Electric Pump

Next, an assembly method of the electric pump 1 is explained in detailwith reference to the attached drawings. An assembly process of theelectric pump 1 is characterized by the resin portion 60 which is formedby insert molding at the stator 32 and the pump housing 11. The otherprocesses such as an assembly of the rotor 36, an assembly of the stator32, an assembly of the control portion 50 and a mounting of the internalgear pump 21 to the pump housing 11, for example, are known andtherefore detailed explanation is omitted.

[Forming Method of Resin Portion]

FIGS. 4 to 8 illustrate a process for forming the resin portion 60 byinsert molding at the stator 32 and the pump housing 11. First, asillustrated in FIGS. 4 and 5, the stator 32 is placed onto a fixed die72 of a forming die 70, the forming die 70 consisting of the fixed die72 and a movable die 78. The fixed die 72 includes a stator contactportion 73 in a column form, a step 74 provided at a lower end of thestator contact portion 73, and a dent 76 provided at an upper surface 75and including a circular cross-section in a direction orthogonal to anaxis of the fixed die 72. Because the fixed die 72 is processed bycutting, for example, processing accuracy is extremely high. Therefore,dimensional accuracy of an outer diameter of the stator contact portion73 and an inner diameter of the dent 76 may increase. In addition, theconcentricity between an axis of the stator contact portion 73 and anaxis of the dent 76 is greatly reduced so that the stator contactportion 73 and the dent 76 are coaxial with each other. In thefollowing, each of the axis of the stator contact portion 73 and theaxis of the dent 76 is referred to as an axis Y.

As illustrated in FIG. 5, in a case where the stator 32 is placed ontothe fixed die 72 while being fitted therein, an inner peripheral surfaceof the stator 32 makes contact with an outer peripheral surface of thestator contact portion 73. Accordingly, an axis of the stator 32 and theaxis Y of the stator contact portion 73 match each other to achievepositioning in the radial direction. In the stator 32, an inner diameterof the coil support frame 35 is slightly greater than an inner diameterof the stator core 33. The step 74 is provided corresponding to adifference between the aforementioned inner diameters. By the placementof the stator 32, an end surface of the stator core 33 makes contactwith the step 74 so that the stator 32 is positioned relative to thefixed die 72 in a direction along the axis Y.

Next, as illustrated in FIGS. 5 and 6, after the stator 32 is placedonto the fixed die 72, the pump housing 11 is placed onto the fixed die72 so that the protruding portion 15 is fitted in the dent 76. The innerdiameter of the dent 76 is substantially equal to an outer diameter ofthe protruding portion 15 of the pump housing 11. By the placement ofthe pump housing 11, an outer peripheral surface of the protrudingportion 15 makes contact with an inner peripheral surface of the dent76. Accordingly, an axis of the pump housing 11 and the axis Y of thefixed die 72 match each other to achieve positioning in the radialdirection. In addition, by the placement of the pump housing 11, asurface at a radially outer side than the protruding portion 15 in thepump housing 11 makes contact with the upper surface 75 so that the pumphousing 11 is positioned relative to the fixed die 72 in the directionalong the axis Y.

In a state illustrated in FIG. 6, the axis of the stator 32 and the axisof the pump housing 11 both match the axis Y of the fixed die 72. Theoutermost diameter of the stator 32 is the same as the outermostdiameter of the pump housing 11.

Next, as illustrated in FIG. 7, the movable die 78 is pressed againstthe fixed die 72 so as to close the forming die. Afterwards, asillustrated in FIG. 8, melted thermoplastic resin such as polyphenylenesulfide (PPS) resin, for example, is brought to flow into the formingdie 70 from a gate 79. When the inside of the forming die 70 is filledwith the thermoplastic resin, the resin is cooled and hardened in theclosed die. The hardened thermoplastic resin forms the resin portion 60.Because the outermost diameter of the stator 32 is the same as theoutermost diameter of the pump housing 11, flow resistance when theresin fills the forming die 70 is small to thereby increase fillingability. In addition, a thickness of the resin portion 60 in the radialdirection thereof may be easily constant. With the constant thickness ofthe resin portion 60, an entire periphery of the resin portion 60 isevenly cooled so that shrinkage of the resin portion 60 may be unlikelyto occur and displacement of the axes of the stator 32 and the pumphousing 11 may be unlikely to occur after cooling of the resin portion60.

Once the thermoplastic resin is hardened, the forming die 70 is openedto take out an intermediate assembly 80 which is obtained by the stator32 and the pump housing 11 which are integrated by the resin portion 60as illustrated in FIG. 9. Even in the state of the intermediate assembly80, the axis of the stator 32 and the axis of the pump housing 11maintain matching each other.

Afterwards, the oil seal 26, the rotor 36 into which the rotary shaft 25is inserted to be positioned, and the internal gear pump 21 areassembled on the intermediate assembly 80. The pump cover 40 is thenjoined to an end portion of the resin portion 60 by welding, forexample. Finally, the control portion 50 is assembled on the resinportion 60 and the cover member 54 is joined to an end portion of theresin portion 60 by welding, for example. As a result, the electric pump1 is completed.

According to the present embodiment, after the stator 32 of the motorportion 30 and the pump housing 11 of the pump portion 10 are placedonto the metallic fixed die 72 in a state where the axis of the stator32 and the axis of the pump housing 11 match the axis Y of the fixed die72, the resin portion 60 is formed by insert molding to integrate thestator 32 and the pump housing 11. Thus, in the intermediate assembly 80obtained after the resin portion 60 is formed, the axis of the stator 32and the axis of the pump housing 11 are maintained matching each other.As a result, the concentricity between the axis of the stator 32 and theaxis of the pump housing 11 at the electric pump 1 is greatly reduced ascompared to the concentricity between an axis of a motor portion and anaxis of a pump portion in a case where the motor portion and the pumpportion are separately produced so that a recess portion and aprojection of the motor portion and the pump portion are fitted in aspigot structure.

In a case where the concentricity between the motor portion 30 and thepump portion 10 decreases, the concentricity between the axis of thestator 32 of the motor portion 30 and an axis of the rotor 36 where therotary shaft 25 is inserted to be positioned within the bearing bore 17of the pump portion 10 decreases. Thus, an air gap between the stator 32and the rotor 36 may decrease to thereby improve driving efficiency ofthe motor. That is, with the same driving efficiency, an amount of usageof the magnet 38 employed at the rotor 36 may decrease.

In addition, the outer peripheral surface of the pump housing 11 made offerrous metallic material is covered by the resin portion 60 so that theouter peripheral surface of the pump housing 11 is inhibited from makingcontact with air. The pump housing 11 is therefore inhibited from beingcorroded. Thus, performance and lifetime of the electric pump 1 areinhibited from decreasing, which may lead to stable performance of theelectric pump 1 for a long period of time.

In the present embodiment, the resin portion 60 extends along the axialdirection to an end surface of the pump housing 11 at a side facing thepump cover 40. Thus, the pump cover 40 formed by the resin is joined tothe resin portion 60 by welding, for example, so that a bolt which isemployed for joining a pump cover at a known electric pump is notnecessary. As a result, in the motor portion 30 and the pump portion 10,a bore through which the bolt is inserted to be positioned or aprotruding portion at a radially outer side where an internal thread isprovided for fixing the bolt is not necessary. The electric pump 1 maybe produced at a reduced cost and a reduced size.

INDUSTRIAL APPLICABILITY

The present invention is applicable to an electric pump and a method forproducing the same.

EXPLANATION OF REFERENCE NUMERALS

-   1 electric pump-   10 pump portion-   11 pump housing-   15 protruding portion-   16 groove portion (recess portion)-   21 internal gear pump (gear pump)-   30 motor-   32 stator-   36 rotor-   60 resin portion-   70 forming die-   72 fixed die-   76 dent-   78 movable die

1: An electric pump comprising: a pump portion including a pump housingand a gear pump which is housed in the pump housing, the pump portionsuctioning and discharging a hydraulic fluid by a rotation of the gearpump; a motor portion arranged adjacent to the pump portion in adirection along an axis of the pump portion and including a rotor whichrotates synchronously with the gear pump and coaxially with the axis,the motor portion including a stator which is arranged at an outerperiphery of the rotor and disposed coaxially with the axis, the statorapplying a rotation drive force to the rotor; and a resin portionintegrally surrounding at least an outer periphery of the pump housingand an outer periphery of the stator. 2: The electric pump according toclaim 1, wherein each of the pump housing and the stator includes acircular outermost configuration as viewed in the direction along theaxis, the pump housing and the stator include same outermost diametersas each other. 3: The electric pump according to claim 1, wherein theresin portion includes a constant thickness in a radial direction of theresin portion. 4: The electric pump according to claim 1, wherein eachof the pump housing and the gear pump is made of a ferrous material. 5:The electric pump according to claim 1, wherein the pump housingincludes a recess portion at an outer surface, the recess portion intowhich resin of the resin portion is fitted. 6: A method for producing anelectric pump, comprising: a step for placing a stator in a cylindricalform onto an outer peripheral surface of a fixed die of a forming die ina state where an inner peripheral surface of the stator makes contactwith the outer peripheral surface of the fixed die, the forming diebeing configured to open and close and including the fixed die and amovable die; a step for placing a pump housing which includes aprotruding portion in a cylindrical form in a state where an outerperipheral surface of the protruding portion makes contact with an innerperipheral surface of a dent which is provided at an upper surface ofthe fixed die, the dent including a circular cross-section in adirection orthogonal to an axis of the fixed die; and a step for forminga resin portion by flowing resin into the forming die to harden theresin after the movable die is pressed against the fixed die to closethe forming die, the resin portion integrally surrounding at least anouter periphery of the pump housing and an outer periphery of thestator.